Defining Mechanisms of Extrinsic Apoptosis in Human Macrophages

Project: Research


  • Neha Nataraj (PI)


The bacterial genus Yersinia is an important cause of illness ranging from food poisoning to plague. Infection can progress to septicemia, where treatment options are limited and serious cardiac complications, including endocarditis, can result. Understanding inflammatory responses to Yersinia will facilitate the development of host-directed therapies to control systemic bacterial infections. Yersinia causes disease by suppressing critical defense responses in immune cells, including NF-kB signaling pathways. We and others have demonstrated that infection of murine macrophages by Yersinia leads to apoptosis that requires activation of receptor interacting protein kinase 1 (RIPK1) and the cysteine-aspartyl protease caspase-8. This pathway is also induced by pharmacological blockade of NF-kB signaling. In mice, inhibition of RIPK1 activity prevents apoptosis and bacterial clearance, resulting in host death. Thus, RIPK1-kinase-induced apoptosis provides protection from infection in mouse models. However, significant differences exist between mice and humans in expression of proteins that regulate apoptosis. Mice possess a single cell extrinsic initiator, caspase-8; humans and all other vertebrates possess two orthologs, CASP8 and -10. Furthermore, murine deficiency in caspase-8 or RIPK1 results in embryonic lethality, whereas humans lacking these components are viable but develop inflammatory disease and exhibit increased susceptibility to infections. These observations indicate a key gap in our knowledge of the human apoptosis pathways. Intriguingly, my preliminary data indicate that apoptosis in human macrophages following NF-kB blockade requires RIPK1 but is independent of its kinase activity, unlike mouse macrophages, which require RIPK1 kinase activity. I therefore hypothesize that human macrophages induce apoptosis in response to bacterial blockade of NF-kB signaling via a unique mechanism that requires RIPK1, CASP8 and -10 but not RIPK1 kinase activity. To test this hypothesis, I will generate a comprehensive panel of human cell lines lacking RIPK1, its kinase activity or specific interacting domains, as well as those lacking CASP8 and/or -10. I will subject them to Yersinia infection and test their ability to undergo apoptosis using assays we have developed. These studies will provide new insight into the molecular basis of apoptosis in human cells, which will aid the development of improved treatment options for bacterial infection.
Award amount$62,032.00
Award date01/01/2020
Program typePredoctoral Fellowship
Award ID20PRE35080173
Effective start/end date01/01/202012/31/2021